Fluorine-containing ether compound, lubricant for magnetic recording medium, and magnetic recording medium

ABSTRACT

A fluorine-containing ether compound represented by the following formula (1) is provided.(In the formula (1), R1 is an alkoxy group having 1 to 10 carbon atoms, R2 is a perfluoropolyether chain, R3 is —OCH2CH(OH)CH2O(CH2)mOH (m in the formula is an integer of 2 to 4).)

TECHNICAL FIELD

The present invention relates to a fluorine-containing ether compoundpreferable for application as a lubricant for magnetic recording media,a lubricant for a magnetic recording medium containing the same, and amagnetic recording medium.

Priority is claimed on Japanese Patent Application No. 2019-141290,filed in Japan on Jul. 31, 2019, the content of which is incorporatedherein by reference.

BACKGROUND ART

Development of magnetic recording media suitable for a high recordingdensity is underway to improve the recording density of magneticrecording/reproducing devices.

Conventionally, there have been magnetic recording media having arecording layer formed on a substrate and a protective layer made ofcarbon or the like formed on the recording layer. The protective layerprotects information recorded in the recording layer and enhances thesliding properties of a magnetic head. However, the protective layerprovided on the recording layer is not sufficient for magnetic recordingmedia to obtain sufficient durability. Therefore, it is common to form alubricating layer on the surface of the protective layer by applying alubricant.

As the lubricant that is used at the time of forming the lubricatinglayer in magnetic recording media, for example, lubricants containing acompound having a polar group such as a hydroxy group at a terminal of afluorine-based polymer having a repeating structure containing CF₂ havebeen proposed.

For example, Patent Document 1 discloses a fluoropolyether compoundhaving an alkoxy group at one terminal and having a hydroxy group at theother terminal. In addition, Patent Document 2 discloses a compound inwhich a substituent is disposed in which a plurality of hydroxyl groupsis present at both terminal portions and the shortest distance betweenthe hydroxyl groups is three atoms or more.

CITATION LIST Patent Document Patent Document 1

International Publication WO 2015/199037

Patent Document 2

Japanese Patent No. 4632144

SUMMARY OF INVENTION Technical Problem

There is a demand for a further decrease in the flying height of amagnetic head in magnetic recording/reproducing devices. This requires afurther decrease in the thickness of lubricating layers in magneticrecording media.

However, ordinarily, there is a tendency that a decrease in thethickness of lubricating layers degrades the coatability of lubricatinglayers and thereby degrades the chemical substance resistance and wearresistance of magnetic recording media.

The present invention has been made in consideration of theabove-described circumstances, and an objective of the present inventionis to provide a fluorine-containing ether compound that is capable offorming lubricating layers having excellent chemical substanceresistance and wear resistance in spite of a thin thickness and can bepreferably used as a material for lubricants for magnetic recordingmedia.

In addition, another objective of the present invention is to provide alubricant for a magnetic recording medium containing thefluorine-containing ether compound of the present invention.

In addition, still another objective of the present invention is toprovide a magnetic recording medium having a lubricating layercontaining the fluorine-containing ether compound of the presentinvention and having excellent reliability and durability.

Solution to Problem

The present inventors repeated intensive studies to solve theabove-described problem.

As a result, the present inventors found that a fluorine-containingether compound having a specific structure in which an alkoxy grouphaving 1 to 10 carbon atoms is present at one terminal of aperfluoropolyether chain and —OCH₂CH(OH)CH₂O(CH₂)_(m)OH (m in theformula is an integer of 2 to 4) is present at the other terminal ispreferable and obtained the idea of the present invention.

That is, the present invention relates to the following matters.

A compound of a first aspect of the present invention is the followingcompound.

[1] A fluorine-containing ether compound represented by the followingformula (1).

(In the formula (1), R¹ is an alkoxy group having 1 to 10 carbon atoms,R² is a perfluoropolyether chain, R³ is —OCH₂CH(OH)CH₂O(CH₂)_(m)OH (m inthe formula is an integer of 2 to 4).)

The compound of the first aspect of the present invention preferably hascharacteristics to be described in the following [2] to [4]. Two or moreof the following characteristics are also preferably combined together.

[2] The fluorine-containing ether compound according to [1], in which R²in the formula (1) is represented by any one of the following formulae(2) to (4).

(In the formula (2), p represents 1 to 30, and q represents 0 to 30.)

(In the formula (3), r represents 1 to 30.)

(In the formula (4), s represents 1 to 20.)

[3] The fluorine-containing ether compound according to [1] that is anyone of compounds represented by the following formulae (A) to (F).

(In the formula (A), p represents 1 to 30, and q represents 0 to 30.)

(In the formula (B), r represents 1 to 30.)

(In the formula (C), s represents 1 to 20.)

(In the formula (D), p represents 1 to 30, and q represents 0 to 30.)

(In the formula (E), p represents 1 to 30, and q represents 0 to 30.)

(In the formula (F), p represents 1 to 30, and q represents 0 to 30.)

[4] The fluorine-containing ether compound according to any one of [1]to [3], in which a number-average molecular weight thereof is in a rangeof 500 to 10000.

A second aspect of the present invention is the following lubricant fora magnetic recording medium.

A lubricant for a magnetic recording medium containing thefluorine-containing ether compound according to any one of [1] to [4].

A third aspect of the present invention is the following magneticrecording medium.

A magnetic recording medium including at least a magnetic layer, aprotective layer and a lubricating layer sequentially provided on asubstrate, in which the lubricating layer contains thefluorine-containing ether compound according to any one of [1] to [4].

The magnetic recording medium according to [6], in which the lubricatinglayer has an average film thickness of 0.5 nm to 3 nm.

Advantageous Effects of Invention

The fluorine-containing ether compound of the present invention ispreferably used as a material for lubricants for magnetic recordingmedia.

The lubricant for a magnetic recording medium of the present inventioncontains the fluorine-containing ether compound of the present inventionand is thus capable of forming lubricating layers capable of obtainingexcellent chemical substance resistance and wear resistance in spite ofa thin thickness.

The magnetic recording medium of the present invention is provided witha lubricating layer having excellent chemical substance resistance andwear resistance and thus has excellent reliability and durability.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic cross-sectional view showing a preferable exampleof an embodiment of a magnetic recording medium of the presentinvention.

DESCRIPTION OF EMBODIMENTS

Hereinafter, a fluorine-containing ether compound, a lubricant for amagnetic recording medium (hereinafter, abbreviated as “lubricant” insome cases) and a magnetic recording medium of the present inventionwill be described in detail. The present invention is not limited onlyto an embodiment to be described below.

The present embodiment is simply a specific description for betterunderstanding of the gist of the invention and does not limit thepresent invention unless particularly otherwise specified. Numericalvalues, orders, times, ratios, materials, amounts, configurations andthe like can be modified, added, omitted, substituted and the likewithin the scope of the gist of the present invention.

Fluorine-Containing Ether Compound

A fluorine-containing ether compound of the present embodiment isrepresented by the following formula (1).

(In the formula (1), R¹ is an alkoxy group having 1 to 10 carbon atoms,R² is a perfluoropolyether chain, R³ is —OCH₂CH(OH)CH₂O(CH₂)_(m)OH (m inthe formula is an integer of 2 to 4).)

Here, the reason that excellent chemical substance resistance and wearresistance can be obtained in spite of a thin thickness in a case wherea lubricating layer is formed on a protective layer of a magneticrecording medium using a lubricant containing the fluorine-containingether compound of the present embodiment will be described.

As shown in the formula (1), the fluorine-containing ether compound ofthe present embodiment has a perfluoropolyether chain represented by R²(hereinafter, abbreviated as “PFPE chain” in some cases). The PFPE chaincoats the surface of a protective layer and also imparts lubricity to alubricating layer to reduce a friction force between a magnetic head andthe protective layer when the lubricating layer is formed by applying alubricant containing the fluorine-containing ether compound onto theprotective layer.

In addition, as shown in the formula (1), the alkoxy group having 1 to10 carbon atoms represented by R¹ bonds to one terminal of the PFPEchain represented by R². The alkoxy group having 1 to 10 carbon atomsrepresented by R¹ improves chemical substance resistance and wearresistance in the lubricating layer containing the fluorine-containingether compound of the present embodiment through the intermolecularinteraction of the alkoxy groups and/or the interaction between thealkoxy group and the protective layer. Therefore, the lubricating layercontaining the fluorine-containing ether compound of the presentembodiment has excellent chemical substance resistance and wearresistance compared with, for example, lubricating layers containing afluorine-containing ether compound in which a hydroxy group is disposedin place of the alkoxy group having 1 to 10 carbon atoms represented byR¹.

In addition, as shown in the formula (1), —OCH₂CH(OH)CH₂O(CH₂)_(m)OH (min the formula is an integer of 2 to 4) represented by R³ bonds to theother terminal of the PFPE chain represented by R². Two hydroxy groups(—OH) that are included in the terminal group represented by R³ closelyattach the fluorine-containing ether compound and the protective layerin the lubricating layer containing the fluorine-containing ethercompound of the present embodiment and thereby improve chemicalsubstance resistance.

In addition, in the terminal group represented by R³, the two hydroxygroups bond to different carbon atoms, and the carbon atoms to which thehydroxy groups bond are bonded to each other through a linking groupincluding an oxygen atom (a linking group including -O- (ether bond)).The linking group including the ether bond imparts flexibility to theterminal group represented by R³. Therefore, compared with, for example,a fluorine ether compound in which two hydroxy groups that are includedin a terminal group bond to different carbon atoms, and the carbon atomsto which the hydroxy groups bond are bonded to each other, thelubricating layer containing the fluorine-containing ether compound ofthe present embodiment is easily adsorbed to the protective film and isexcellent in terms of adhesion between the lubricating layer and theprotective layer.

From this fact, it is assumed that a lubricant containing thefluorine-containing ether compound of the present embodiment is capableof coating the surface of the protective layer at a high coating rate inspite of a thin thickness and capable of forming a lubricating layerhaving excellent chemical substance resistance and wear resistance.

In the fluorine-containing ether compound of the present embodimentrepresented by the formula (1), R² is the perfluoropolyether chain (PFPEchain). R² is not particularly limited and can be appropriately selecteddepending on performance or the like required for lubricants containingthe fluorine-containing ether compound.

R² is preferably represented by any one of the following formula (2) toformula (4). In a case where R² is represented by any one of the formula(2) to formula (4), the synthesis of the fluorine-containing ethercompound is easy, which is preferable.

In addition, in a case where R² is represented by any one of the formula(2) to formula (4), the ratio of the number of oxygen atoms (the numberof the ether bonds (-O-)) to the number of carbon atoms in theperfluoropolyether chain is appropriate. Therefore, afluorine-containing ether compound having appropriate hardness isobtained. Therefore, the fluorine-containing ether compound applied ontothe protective layer is less likely to aggregate on the protectivelayer, and it is possible to form a lubricating layer having a thinnerthickness at a sufficient coating rate. In addition, in a case where R²is represented by any one of the formula (2) to formula (4), thefluorine-containing ether compound becomes capable of providinglubricating layers having favorable wear resistance.

(In the formula (2), p represents 1 to 30, and q represents 0 to 30.)

(In the formula (3), r represents 1 to 30.)

(In the formula (4), s represents 1 to 20.)

In the formula (2), the arrangement sequence of (CF₂—CF₂—O) and (CF₂—O),which are repeating units, is not particularly limited. In the formula(2), the number p of (CF₂—CF₂—O)’_(S) and the number q of (CF₂—O)’s maybe equal to each other or may be different from each other. The formula(2) may include any of a random copolymer, a block copolymer, and analternating copolymer composed of the monomer units (CF₂—CF₂—O) and(CF₂—O).

In a case where R² in the formula (1) is the formula (2), p thatindicates the average degree of polymerization is 1 to 30, preferably 1to 20 and more preferably 1 to 15. p may be 3 to 7 or 7 to 13 asnecessary. In a case where R² in the formula (1) is the formula (2), qthat indicates the average degree of polymerization is 0 to 30,preferably 0 to 20 and more preferably 0 to 15. q may be 3 to 7 or 7 to13 as necessary. In addition, in a case where q is 0, p is preferably 1to 17.

In a case where r that indicates the average degree of polymerization is1 to 30 in the formula (3), the number-average molecular weight of thefluorine-containing ether compound of the present embodiment is likelyto be within a preferable range. r is preferably 2 to 20 and morepreferably 3 to 10.

In a case where s that indicates the average degree of polymerization is1 to 20 in the formula (4), the number-average molecular weight of thefluorine-containing ether compound of the present embodiment is likelyto be within a preferable range. s is preferably 2 to 15 and morepreferably 2 to 8.

In the formula (1), R¹ is an alkoxy group having 1 to 10 carbon atomsand preferably an alkoxy group having 1 to 7 carbon atoms. In addition,R¹ is preferably a linear alkoxy group having 1 to 10 carbon atoms.Specific examples of R¹ include a methoxy group, an ethoxy group, apropoxy group, a butoxy group, a pentoxy group, a hexoxy group, aheptoxy group, an octoxy group, a nonoxy group, a decoxy group and thelike.

In the formula (1), R³ is —OCH₂CH(OH)CH₂O(CH₂)_(m)OH (m in the formulais an integer of 2 to 4).

The fluorine-containing ether compound represented by the formula (1)is, specifically, preferably any one of the compounds represented by theformulae (A) to (F). p, q, r and s in the formulae (A) to (F) are valuesindicating the average degree of polymerization and thus do notnecessarily need to be integers.

In the compounds represented by the formulae (A), (E) and (F), R¹ is analkoxy group having three carbon atoms, and R² is the formula (2). Inaddition, m in R³ is 2 in the compound represented by the formula (A), min R³ is 3 in the compound represented by the formula (E), and m in R³is 4 in the compound represented by the formula (F).

In the compound represented by the formula (B), R¹ is an alkoxy grouphaving three carbon atoms, R² is the formula (3), and m in R³ is 2.

In the compound represented by the formula (C), R¹ is an alkoxy grouphaving three carbon atoms, R² is the formula (4), and m in R³ is 2.

In the compound represented by the formula (D), R¹ is an alkoxy grouphaving seven carbon atoms, R² is the formula (2), and m in R³ is 2.

(In the formula (A), p represents 1 to 30, and q represents 0 to 30.)

(In the formula (B), r represents 1 to 30.)

(In the formula (C), s represents 1 to 20.)

(In the formula (D), p represents 1 to 30, and q represents 0 to 30.)

(In the formula (E), p represents 1 to 30, and q represents 0 to 30.)

(In the formula (F), p represents 1 to 30, and q represents 0 to 30.)

When the compound represented by the formula (1) is any one of thecompounds represented by the formulae (A) to (F), a raw material is easyto procure, and furthermore, it is possible to form lubricating layersfrom which superior chemical substance resistance and wear resistancecan be obtained in spite of a thin thickness, which is preferable.

The number-average molecular weight (Mn) of the fluorine-containingether compound of the present embodiment is preferably within a range of500 to 10000. When the number-average molecular weight is 500 or more,the evaporation of lubricants containing the fluorine-containing ethercompound of the present embodiment is less likely to occur, and it ispossible to prevent lubricants from being evaporated and transferred toa magnetic head. The number-average molecular weight of thefluorine-containing ether compound is more preferably 1000 or more. Inaddition, when the number-average molecular weight is 10000 or less, theviscosity of the fluorine-containing ether compound becomes appropriate,and it is possible to easily form lubricating layers having a thinthickness by applying lubricants containing the fluorine-containingether compound. The number-average molecular weight of thefluorine-containing ether compound is preferably 3000 or less in orderto obtain a viscosity that makes lubricants to which thefluorine-containing ether compound is applied easily handleable.

The number-average molecular weight (Mn) of the fluorine-containingether compound is a value measured by ¹H-NMR and ¹⁹F-NMR, specifically,¹H-NMR and ¹⁹F-NMR with AVANCE III400 manufactured by Bruker BioSpinGroup. In the nuclear magnetic resonance (NMR) measurement, a specimenis diluted with a single or mixed solvent of hexafluorobenzene,acetone-d, tetrahydrofuran-d and the like and used in the measurement.As the reference of the ¹⁹F-NMR chemical shift, the peak ofhexafluorobenzene was set to -164.7 ppm, and, as the reference of the¹H-NMR chemical shift, the peak of acetone was set to 2.2 ppm.

Production Method

A method for producing the fluorine-containing ether compound of thepresent embodiment is not particularly limited, and thefluorine-containing ether compound can be produced using a well-knownconventional production method. The fluorine-containing ether compoundof the present embodiment can be produced using, for example, aproduction method to be described below.

First, an addition reaction of an alkyl halide having 1 to 10 carbonatoms with a compound having a perfluoropolyether chain corresponding toRin the formula (1) is conducted. This generates a compound representedby a formula (1-1).

(In the formula (1-1), R¹ and R² are the same as in the formula (1).)

Examples of the alkyl halide having 1 to 10 carbon atoms that is used inthe addition reaction include 1-bromopropane, 1-chloropropane,1-iodopropane, 1-bromobutane, 1-chlorobutane, 1-iodobutane,1-bromopentane, 1-chloropentane, 1-iodopentane, 1-bromohexane,1-chlorohexane, 1-iodohexane, 1-bromoheptane, 1-chloroheptane,1-iodoheptane, 1-bromooctane, 1-chlorooctane, 1-iodooctane,1-bromononane, 1-chlorononane, 1-iodononane, 1- bromodecane,1-chlorodecane, 1-iododecane and the like.

Next, the compound represented by the formula (1-1) and epichlorohydrinor epibromohydrin are reacted with each other, thereby generatingperfluoropolyether having an alkoxy group and an epoxy group.Furthermore, the perfluoropolyether having an alkoxy group and an epoxygroup and any one selected from ethylene glycol, 1,3-propanediol and1,4-butanediol are reacted with each other. A compound obtained asdescribed above can be separated using, for example, a method in whichcolumn chromatography is used.

The fluorine-containing ether compound represented by the formula (1)can be obtained by the above-described method.

The fluorine-containing ether compound of the present embodiment is acompound represented by the formula (1). Therefore, when a lubricatinglayer is formed on a protective layer using a lubricant containing thisfluorine-containing ether compound, the surface of the protective layeris coated with the PFPE chain represented by R² in the formula (1), anda friction force between a magnetic head and the protective layer isreduced. In addition, in the lubricating layer formed using thelubricant containing the fluorine-containing ether compound of thepresent embodiment, chemical substance resistance and wear resistancecan be obtained through the intermolecular interaction provided by thealkoxy group represented by R¹ and/or the interaction between the alkoxygroup and the protective layer.

In addition, the fluorine-containing ether compound of the presentembodiment is closely attached onto the protective layer due to bondsbetween the two hydroxy groups that are included in the terminal grouprepresented by R³ and the protective layer. Furthermore, the two hydroxygroups that are included in the terminal group represented by R³ bond todifferent carbon atoms, and the carbon atoms to which the hydroxy groupsbond are bonded to each other through a linking group including anoxygen atom. Therefore, the lubricating layer containing the fluorineether compound of the present embodiment has favorable flexibility.Therefore, the lubricating layer containing the fluorine ether compoundof the present embodiment is easily adsorbed to the protective film andhas excellent adhesion to the protective layer.

As described above, according to the fluorine-containing ether compoundof the present embodiment, the lubricating layer and the protectivelayer are strongly bonded to each other, and a lubricating layer havingexcellent chemical substance resistance and wear resistance can beobtained.

Lubricant for Magnetic Recording Medium

A lubricant for a magnetic recording medium of the present embodimentcontains the fluorine-containing ether compound represented by theformula (1).

The lubricant of the present embodiment can be used after being mixed asnecessary with a well-known material that is used as a material forlubricants as long as characteristics attributed to thefluorine-containing ether compound represented by the formula (1)contained in the lubricant are not impaired.

Specific examples of a well-known material include FOMBLIN (registeredtrademark) ZDIAC, FOMBLIN ZDEAL, FOMBLIN AM-2001 (all manufactured bySolvay Solexis), Moresco A20H (manufactured by Moresco Corporation) andthe like. The number-average molecular weight of the well-known materialthat is used by being mixed with the lubricant of the present embodimentis preferably 1000 to 10000.

In a case where the lubricant of the present embodiment contains amaterial other than the fluorine-containing ether compound representedby the formula (1), the content of the fluorine-containing ethercompound represented by the formula (1) in the lubricant of the presentembodiment is preferably 50 mass% or more and more preferably 70 mass%or more. The content may be 80 mass% or more, 90 mass% or more or 95mass% or more.

The lubricant of the present embodiment contains the fluorine-containingether compound represented by the formula (1) and is thus capable ofcoating the surface of protective layers at a high coating rate in spiteof a thin thickness and capable of forming lubricating layers havingexcellent adhesion to protective layers. Therefore, according to thelubricant of the present embodiment, lubricating layers having excellentchemical substance resistance and wear resistance can be obtained inspite of a thin thickness.

In addition, the lubricant of the present embodiment contains thefluorine-containing ether compound represented by the formula (1), andthus excellent chemical substance resistance and wear resistance can beobtained through the intermolecular interaction provided by the alkoxygroup represented by R¹ in the formula (1) and/or the interactionbetween the alkoxy group and the protective layer.

Magnetic Recording Medium

A magnetic recording medium of the present embodiment is sequentiallyprovided with at least a magnetic layer, a protective layer and alubricating layer on a substrate.

In the magnetic recording medium of the present embodiment, a singleunderlayer or two or more underlayers can be provided as necessarybetween the substrate and the magnetic layer. In addition, it is alsopossible to provide an adhesive layer and/or a soft magnetic layerbetween the underlayer and the substrate.

FIG. 1 is a schematic cross-sectional view showing an embodiment of themagnetic recording medium of the present invention.

A magnetic recording medium 10 of the present embodiment has a structurein which an adhesive layer 12, a soft magnetic layer 13, a firstunderlayer 14, a second underlayer 15, a magnetic layer 16, a protectivelayer 17 and a lubricating layer 18 are sequentially provided on asubstrate 11.

Substrate

The substrate 11 can be arbitrarily selected, and it is possible to use,for example, a non-magnetic substrate or the like wherein a NiP or NiPalloy film is formed on a base made of a metal or alloy material such asAI or an AI alloy.

In addition, as the substrate 11, a non-magnetic substrate made of anon-metal material such as glass, ceramic, silicon, silicon carbide,carbon or resin may be used, and a non-magnetic substrate wherein a NiPor NiP alloy film is formed on a base made of this non-metal materialmay be used.

Adhesive Layer

The adhesive layer 12 prevents the progress of corrosion of thesubstrate 11 which may occur in a case where the substrate 11 and thesoft magnetic layer 13, which is provided on the adhesive layer 12, aredisposed in direct contact with each other.

The material of the adhesive layer 12 can be arbitrarily selected andcan be appropriately selected from, for example, Cr, a Cr alloy, Ti, aTi alloy, CrTi, NiAl, an AIRu alloy and the like. The adhesive layer 12can be formed by, for example, a sputtering method.

Soft Magnetic Layer

The soft magnetic layer 13 can be arbitrarily selected and preferablyhas a structure in which, for example, a first soft magnetic film, aninterlayer made of a Ru film and a second soft magnetic film aresequentially laminated. That is, the soft magnetic layer 13 preferablyhas a structure in which the interlayer made of a Ru film is sandwichedbetween two soft magnetic films and thereby the soft magnetic films onand under the interlayer are antiferromagnetically coupled (AFC).

Examples of the material of the first soft magnetic film and the secondsoft magnetic film include a CoZrTa alloy, a CoFe alloy and the like.

To the CoFe alloy that is used for the first soft magnetic film and thesecond soft magnetic film, any of Zr, Ta and Nb is preferably added.This accelerates the amorphization of the first soft magnetic film andthe second soft magnetic film, makes it possible to improve theorientation of the first underlayer (seed layer) and makes it possibleto reduce the flying height of a magnetic head.

The soft magnetic layer 13 can be formed by, for example, a sputteringmethod.

First Underlayer

The first underlayer 14 is a layer for controlling the orientations orcrystal sizes of the second underlayer 15 and the magnetic layer 16 thatare provided on the first underlayer 14.

Examples of the first underlayer 14 include a Cr layer, a Ta layer, a Rulayer, an alloy layer of CrMo, CoW, CrW, CrV or CrTi, and the like.

The first underlayer 14 can be formed by, for example, a sputteringmethod.

Second Underlayer

The second underlayer 15 is a layer to control the orientation of themagnetic layer 16 to be favorable. The second underlayer 15 ispreferably a Ru or Ru alloy layer.

The second underlayer 15 may be a single layer or may be composed of aplurality of layers. In a case where the second underlayer 15 iscomposed of a plurality of layers, all of the layers may be made of thesame material or at least one layer may be made of a different material.

The second underlayer 15 can be formed by, for example, a sputteringmethod.

Magnetic Layer

The magnetic layer 16 is made of a magnetic film in which the easymagnetization axis is directed in a perpendicular or parallel directionwith respect to the substrate surface. The magnetic layer 16 is a layercontaining Co and Pt and may be a layer further containing an oxideand/or Cr, B, Cu, Ta, Zr or the like in order to improve SNRcharacteristics.

Examples of the oxide that is contained in the magnetic layer 16 includeSiO₂, SiO, Cr₂O₃, CoO, Ta₂O₃, TiO₂ and the like.

The magnetic layer 16 may be composed of a single layer or may becomposed of a plurality of magnetic layers made of materials withdifferent compositions.

For example, in a case where the magnetic layer 16 is composed of threelayers of a first magnetic layer, a second magnetic layer and a thirdmagnetic layer sequentially laminated from below, the first magneticlayer is preferably a granular structure made of a material containingCo, Cr and Pt and further containing an oxide. As the oxide that iscontained in the first magnetic layer, for example, oxides of Cr, Si,Ta, AI, Ti, Mg, Co or the like are preferably used. Among them, inparticular, TiO₂, Cr₂O₃, SiO₂ and the like can be preferably used. Inaddition, the first magnetic layer is preferably composed of a compositeoxide to which two or more oxides have been added. Among them, inparticular, Cr₂O₃—SiO₂, Cr₂O₃—TiO₂, SiO₂—TiO₂ and the like can bepreferably used.

The first magnetic layer may contain, in addition to Co, Cr, Pt and theoxide, one or more elements selected from B, Ta, Mo, Cu, Nd, W, Nb, Sm,Tb, Ru and Re.

For the second magnetic layer, the same material as the first magneticlayer can be used. The second magnetic layer is preferably a granularstructure.

The third magnetic layer preferably has a non-granular structure made ofa material containing Co, Cr and Pt but containing no oxides. The thirdmagnetic layer may contain, in addition to Co, Cr, and Pt, one or moreelements selected from B, Ta, Mo, Cu, Nd, W, Nb, Sm, Tb, Ru, Re and Mn.

In a case where the magnetic layer 16 is formed of a plurality ofmagnetic layers, a non-magnetic layer is preferably provided between themagnetic layers adjacent to each other. In a case where the magneticlayer 16 is composed of three layers of the first magnetic layer, thesecond magnetic layer and the third magnetic layer, it is preferable toprovide a non-magnetic layer between the first magnetic layer and thesecond magnetic layer and a non-magnetic layer between the secondmagnetic layer and the third magnetic layer.

For the non-magnetic layer that is provided between the magnetic layersadjacent to each other in the magnetic layer 16, it is possible topreferably use, for example, Ru, a Ru alloy, a CoCr alloy, a CoCrXIalloy (XI represents one or more elements selected from Pt, Ta, Zr, Re,Ru, Cu, Nb, Ni, Mn, Ge, Si, O, N, W, Mo, Ti, V and B) and the like.

For the non-magnetic layer that is provided between the magnetic layersadjacent to each other in the magnetic layer 16, an alloy materialcontaining an oxide, a metallic nitride or a metallic carbide ispreferably used. Specifically, as the oxide, for example, SiO₂, Al₂O₃,Ta₂O₅, Cr₂O₃, MgO, Y₂O₃, TiO₂ and the like can be used. As the metallicnitride, for example, AIN, Si₃N₄, TaN, CrN and the like can be used. Asthe metallic carbide, for example, TaC, BC, SiC and the like can beused.

The non-magnetic layer can be formed by, for example, a sputteringmethod.

The magnetic layer 16 is preferably a magnetic layer of perpendicularmagnetic recording in which the easy magnetization axis is directed in aperpendicular direction with respect to the substrate surface in orderto realize a higher recording density. The magnetic layer 16 may be amagnetic layer of longitudinal magnetic recording.

The magnetic layer 16 may be formed by any well-known conventionalmethod such as a deposition method, an ion beam sputtering method or amagnetron sputtering method. The magnetic layer 16 is normally formed bya sputtering method.

Protective Layer

The protective layer 17 protects the magnetic layer 16. The protectivelayer 17 may be composed of a single layer or may be composed of aplurality of layers. As the material of the protective layer 17, carbon,nitrogen-containing carbon, silicon carbide and the like can beexemplified.

As the protective layer 17, a carbon-based protective layer can bepreferably used, and, in particular, an amorphous carbon protectivelayer is preferred. When the protective layer 17 is a carbon-basedprotective layer, the interaction with the hydroxy groups that areincluded in the fluorine-containing ether compound in the lubricatinglayer 18 is further enhanced, which is preferable.

The adhesive force between the carbon-based protective layer and thelubricating layer 18 can be controlled by forming the carbon-basedprotective layer with hydrogenated carbon and/or nitrogenated carbon andadjusting the hydrogen content and/or the nitrogen content in thecarbon-based protective layer. The hydrogen content in the carbon-basedprotective layer is preferably 3 to 20 atom% when measured by thehydrogen forward scattering method (HFS). In addition, the nitrogencontent in the carbon-based protective layer is preferably 4 to 15 atom%when measured by X-ray photoelectron spectroscopy (XPS).

The hydrogen and/or nitrogen that are contained in the carbon-basedprotective layer do not need to be uniformly contained throughout theentire carbon-based protective layer. The carbon-based protective layeris preferably formed as a composition gradient layer in which nitrogenis contained in the lubricating layer 18 side of the protective layer 17and hydrogen is contained in the magnetic layer 16 side of theprotective layer 17. In this case, the adhesive forces between themagnetic layer 16 and the carbon-based protective layer and between thelubricating layer 18 and the carbon-based protective layer furtherimprove.

The film thickness of the protective layer 17 is preferably set to 1 nmto 7 nm. When the film thickness of the protective layer 17 is 1 nm ormore, the performance of the protective layer 17 can be sufficientlyobtained. The film thickness of the protective layer 17 is preferably 7nm or less from the viewpoint of reduction in the thickness of theprotective layer 17.

As a method for forming the protective layer 17, it is possible to use asputtering method in which a carbon-containing target material is used,a chemical vapor deposition (CVD) method in which a hydrocarbon rawmaterial such as ethylene or toluene is used, an ion beam deposition(IBD) method and the like.

In the case of forming the carbon-based protective layer as theprotective layer 17, the carbon-based protective layer can be formed by,for example, a DC magnetron sputtering method. Particularly, in the caseof forming the carbon-based protective layer as the protective layer 17,an amorphous carbon protective layer is preferably formed by a plasmaCVD method. The amorphous carbon protective layer formed by the plasmaCVD method has a uniform surface with small roughness.

Lubricating Layer

The lubricating layer 18 prevents contamination of the magneticrecording medium 10. In addition, the lubricating layer 18 reduces afriction force of a magnetic head of a magnetic recording/reproducingdevice, which slides on the magnetic recording medium 10, and therebyimproves the durability of the magnetic recording medium 10.

The lubricating layer 18 is formed in contact with the protective layer17 as shown in FIG. 1 . The lubricating layer 18 contains theabove-described fluorine-containing ether compound.

In a case where the protective layer 17, which is disposed below thelubricating layer 18, is the carbon-based protective layer, thelubricating layer 18 is bonded to the protective layer 17 with aparticularly high bonding force. As a result, it becomes easy to obtainthe magnetic recording medium 10 in which the surface of the protectivelayer 17 is coated with the lubricating layer 18 at a high coating ratein spite of a thin thickness thereof, and it is possible to effectivelyprevent contamination on the surface of the magnetic recording medium10.

The average film thickness of the lubricating layer 18 can bearbitrarily selected, but is preferably 0.5 nm (5 Å) to 3 nm (30 Å) andmore preferably 0.5 nm (5 Å) to 1 nm (10 Å). When the average filmthickness of the lubricating layer 18 is 0.5 nm or more, the lubricatinglayer 18 does not become an island shape or a mesh shape and is formedin a uniform film thickness. Therefore, the surface of the protectivelayer 17 can be coated with the lubricating layer 18 at a high coatingrate. In addition, when the average film thickness of the lubricatinglayer 18 is 3 nm or less, it is possible to sufficiently reduce thethickness of the lubricating layer 18 and to sufficiently decrease theflying height of a magnetic head.

In a case where the surface of the protective layer 17 is notsufficiently coated with the lubricating layer 18 at a high coatingrate, an environmental substance adsorbed to the surface of the magneticrecording medium 10 passes through voids in the lubricating layer 18 andintrudes into the layer below the lubricating layer 18. Theenvironmental substance that has intruded into the layer below thelubricating layer 18 is adsorbed and bonded to the protective layer 17and generates a contamination substance. In addition, at the time ofreproducing magnetic records, this contamination substance (aggregatedcomponent) adheres (transfers) to a magnetic head as a smear to breakthe magnetic head or degrade the magnetic recording/reproducingcharacteristics of magnetic recording/reproducing devices.

Examples of the environmental substance that generates the contaminationsubstance include a siloxane compound (cyclic siloxane or linearsiloxane), an ionic impurity, a hydrocarbon having a relatively highmolecular weight such as octacosane, a plasticizer such as dioctylphthalate and the like. Examples of a metal ion that is contained in theionic impurity include a sodium ion, a potassium ion and the like.Examples of an inorganic ion that is contained in the ionic impurityinclude a chlorine ion, a bromine ion, a nitrate ion, a sulfate ion, anammonium ion and the like. Examples of an organic ion that is containedin the ionic impurity include an oxalate ion, a formate ion and thelike.

Method for Forming Lubricating Layer

Examples of a method for forming the lubricating layer 18 include amethod in which a magnetic recording medium that is not yet fullymanufactured and thus includes the individual layers up to theprotective layer 17 formed on the substrate 11 is prepared and asolution for forming the lubricating layer is applied and dried on theprotective layer 17.

The solution for forming the lubricating layer can be obtained bydispersing and dissolving the lubricant for a magnetic recording mediumof the above-described embodiment in a solvent that is arbitrarilyselected as necessary and adjusting the viscosity and concentration tobe suitable for the application method.

Examples of the solvent that is used for the solution for forming thelubricating layer include a fluorine-based solvent such as VERTREL(registered trademark) XF (trade name, manufactured by Dupont-MitsuiFluorochemicals Co., Ltd.) and the like.

A method for applying the solution for forming the lubricating layer isnot particularly limited, and examples thereof include a spin coatingmethod, a spraying method, a paper coating method, a dipping method andthe like.

In the case of using the dipping method, it is possible to use, forexample, a method to be described below. First, the substrate 11 onwhich the individual layers up to the protective layer 17 have beenformed is immersed into the solution for forming the lubricating layercontained in an immersion vessel of a dip coater. Next, the substrate 11is lifted from the immersion vessel at a predetermined speed. As aresult, the solution for forming the lubricating layer is applied to thesurface on the protective layer 17 of the substrate 11.

The use of the dipping method makes it possible to uniformly apply thesolution for forming the lubricating layer to the surface of theprotective layer 17 and makes it possible to form the lubricating layer18 on the protective layer 17 in a uniform film thickness.

In the present embodiment, a thermal treatment is preferably carried outon the substrate 11 on which the lubricating layer 18 has been formed.The thermal treatment improves the adhesion between the lubricatinglayer 18 and the protective layer 17 and improves the adhesive forcebetween the lubricating layer 18 and the protective layer 17.

The thermal treatment temperature is preferably set to 100° C. to 180°C. When the thermal treatment temperature is 100° C. or higher, aneffect that improves the adhesion between the lubricating layer 18 andthe protective layer 17 can be sufficiently obtained. In addition, whenthe thermal treatment temperature is set to 180° C. or lower, it ispossible to prevent thermal decomposition of the lubricating layer 18.The thermal treatment time is preferably set to 10 to 120 minutes.

In the present embodiment, a treatment of irradiating the lubricatinglayer 18 on the substrate 11 before the thermal treatment or after thethermal treatment with ultraviolet rays (UV) may be carried out in orderto further improve the adhesive force of the lubricating layer 18 to theprotective layer 17.

The magnetic recording medium 10 of the present embodiment issequentially provided with at least the magnetic layer 16, theprotective layer 17 and the lubricating layer 18 on the substrate 11. Inthe magnetic recording medium 10 of the present embodiment, thelubricating layer 18 containing the above-described fluorine-containingether compound is formed on the protective layer 17 to be in contactwith the protective layer 17. This lubricating layer 18 coats thesurface of the protective layer 17 at a high coating rate in spite of athin thickness. Therefore, in the magnetic recording medium 10 of thepresent embodiment, intrusion of an environmental substance thatgenerates a contamination substance such as an ionic impurity throughvoids in the lubricating layer 18 is prevented. Therefore, only a smallamount of a contamination substance is present on the surface of themagnetic recording medium 10 of the present embodiment. In addition, inthe lubricating layer 18 in the magnetic recording medium 10 of thepresent embodiment, foreign matter (smear) is less likely to begenerated, and pickup can be suppressed. In addition, the lubricatinglayer 18 in the magnetic recording medium 10 of the present embodimenthas excellent wear resistance. Therefore, the magnetic recording medium10 of the present embodiment has excellent reliability and durability.

EXAMPLES

Hereinafter, the present invention will be more specifically describedusing examples and comparative examples. The present invention is notlimited only to the following examples.

Example 1

A compound represented by the following formula (5) was produced by amethod to be described below.

(In the formula (5), p is 4.5 and q is 4.5.)

A compound represented by HOCH₂CF₂O(CF₂CF₂O)_(p)(CF₂O)_(q)CF₂CH₂OH (inthe formula, p is 4.5 and q is 4.5) (number-average molecular weight:1000, molecular weight distribution: 1.1) (20.0 g), 1-bromopropane (1.97g) (molecular weight: 123.0, 16.0 mmol) and t-BuOH (20 mL) were chargedinto a 100 mL eggplant flask in a nitrogen gas atmosphere and stirred atroom temperature until the components became homogeneous. t-BuOK (0.90g) (molecular weight: 112.2, 8.0 mmol) was added to this homogeneousliquid and stirred at 70° C. for 16 hours to be reacted.

An obtained reaction product was cooled to 25° C., moved to a separatoryfunnel containing water (30 mL) and extracted twice with ethyl acetate(80 mL). An organic layer was washed with water and dehydrated withanhydrous sodium sulfate. The drying agent was filtered, the filtratewas then concentrated, and the residue was purified by silica gel columnchromatography, thereby obtaining a compound represented by thefollowing formula (6) (8.20 g) (molecular weight: 1040, 7.9 mmol).

(In the formula (6), p is 4.5 and q is 4.5.)

Next, the compound represented by the formula (6) (8.00 g),epibromohydrin (1.05 g) (molecular weight: 137.0, 7.7 mmol) and t-BuOH(15 mL) were charged into an eggplant flask and stirred at roomtemperature until the components became homogeneous. t-BuOK (0.86 g)(molecular weight: 112.2, 7.7 mmol) was added to this homogeneous liquidand stirred at 70° C. for six hours to be reacted.

An obtained reaction product was cooled to 25° C., moved to a separatoryfunnel containing water (30 mL) and extracted twice with ethyl acetate(80 mL). An organic layer thereof was washed with water and dehydratedwith anhydrous sodium sulfate. The drying agent was filtered, thefiltrate was then concentrated, and the residue was purified by silicagel column chromatography, thereby obtaining a compound represented bythe following formula (7) (5.20 g) (molecular weight: 1103, 4.7 mmol).

(In the formula (7), p is 4.5 and q is 4.5.)

Next, the compound represented by the formula (7) (5.0 g), ethyleneglycol (1.12 g) (molecular weight: 62.1, 18.0 mmol) and t-BuOH (30 mL)were charged into an eggplant flask and stirred at room temperatureuntil the components became homogeneous. t-BuOK (0.56 g) (molecularweight: 112.2, 5.0 mmol) was added to this homogeneous liquid andstirred at 70° C. for six hours to be reacted.

An obtained reaction product was cooled to 25° C., moved to a separatoryfunnel containing water (30 mL) and extracted twice with ethyl acetate(80 mL). An organic layer thereof was washed with water and dehydratedwith anhydrous sodium sulfate. The drying agent was filtered, thefiltrate was then concentrated, and the residue was purified by silicagel column chromatography, thereby obtaining a compound represented bythe above-described formula (5) (4.0 g).

¹H-NMR and ¹⁹F-NMR measurement was carried out on the obtained compound(5), and the structure was identified from the following results.

Identification Data

¹H-NMR (acetone-D₆): δ [ppm] 0.90 to 1.20 (3H), 1.60 to 2.00 (2H), 3.55to 4.20 (15H)

¹⁹F-NMR (acetone-D₆): δ [ppm] = -55.5 to -51.5 (9F), -78.5 (2F), -80.5(2F), -91.0 to -88.5 (18F)

Example 2

A compound represented by the following formula (8) (4.0 g) was obtainedin the same manner as in Example 1 except that fluoropolyetherrepresented by HOCH₂CF₂O(CF₂CF₂O)_(p)(CF₂O)_(q)CF₂CH₂OH (in the formula,p is 7.0 and q is 0) (number-average molecular weight: 1000, molecularweight distribution: 1.1) was used in place of the fluoropolyetherrepresented by HOCH₂CF₂O(CF₂CF₂O)_(p)(CF₂O)_(q)CF₂CH₂OH used in Example1 (in the formula, p is 4.5 and q is 4.5).

(In the formula (8), p is 7.0 and q is 0.)

¹H-NMR and ¹⁹F-NMR measurement was carried out on the obtained compound(8), and the structure was identified from the following results.

Identification Data

¹H-NMR (acetone-D₆): δ [ppm] 0.90 to 1.20 (3H), 1.60 to 2.00 (2H), 3.55to 4.20 (15H)

¹⁹F-NMR (acetone-D₆): δ [ppm] = -78.5 (2F), -81.3 (2F), -90.0 to -88.5(28F)

Example 3

A compound represented by the following formula (9) (4.1 g) was obtainedin the same manner as in Example 1 except that fluoropolyetherrepresented by HOCH₂CF₂CF₂O(CF₂CF₂CF₂O)_(r)CF₂CF₂CH₂OH (in the formula,r is 4.5) (number-average molecular weight: 1000, molecular weightdistribution: 1.1) was used in place of the fluoropolyether representedby HOCH₂CF₂O(CF₂CF₂O)_(p)(CF₂O)_(q)CF₂CH₂OH used in Example 1 (in theformula, p is 4.5 and q is 4.5).

(In the formula (9), r is 4.5.)

¹H-NMR and ¹⁹F-NMR measurement was carried out on the obtained compound(9), and the structure was identified from the following results.

Identification Data

¹H-NMR (acetone-D₆): δ [ppm] 0.90 to 1.20 (3H), 1.60 to 2.00 (2H), 3.55to 4.20 (15H)

¹⁹F-NMR (acetone-D₆): δ [ppm] = -84.0 to -83.0 (18F), -86.4 (4F), -124.3(4F), -130.0 to -129.0 (9F)

Example 4

A compound represented by the following formula (10) (3.4 g) wasobtained in the same manner as in Example 1 except that fluoropolyetherrepresented by HOCH₂CF₂CF₂CF₂O(CF₂CF₂CF₂CF₂O)_(S)CF₂CF₂CF₂CH₂OH (in theformula, s is 3.0) (number-average molecular weight: 1000, molecularweight distribution: 1.1) was used in place of the fluoropolyetherrepresented by HOCH₂CF₂O(CF₂CF₂O)_(p)(CF₂O)_(q)CF₂CH₂OH used in Example1 (in the formula, p is 4.5 and q is 4.5).

(In the formula (10), s is 3.0.)

¹H-NMR and ¹⁹F-NMR measurement was carried out on the obtained compound(10), and the structure was identified from the following results.

Identification Data

¹H-NMR (acetone-D₆): δ [ppm] 0.90 to 1.20 (3H), 1.60 to 2.00 (2H), 3.55to 4.20 (15H)

¹⁹F-NMR (acetone-D₆): δ [ppm] = -84.0 to -83.0 (16F), -122.5 (4F),-126.0 (12F), -129.0 to -128.0 (4F)

Example 5

A compound represented by the following formula (11) (4.5 g) wasobtained in the same manner as in Example 1 except that 1-bromoheptanewas used in place of 1-bromopropane used in Example 1.

(In the formula (11), p is 4.5 and q is 4.5.)

¹H-NMR and ¹⁹F-NMR measurement was carried out on the obtained compound(11), and the structure was identified from the following results.

Identification Data

¹H-NMR (acetone-D₆): δ [ppm] 0.90 to 1.20 (3H), 1.60 to 2.00 (10H), 3.55to 4.20 (15H)

¹⁹F-NMR (acetone-D₆): δ [ppm] = -55.5 to -51.5 (9F), -78.5 (2F), -80.5(2F), -91.0 to -88.5 (18F)

Example 6

A compound represented by the following formula (12) (4.0 g) wasobtained in the same manner as in Example 1 except that 1,3-propanediolwas used in place of ethylene glycol used in Example 1.

(In the formula (12), p is 4.5 and q is 4.5.)

¹H-NMR and ¹⁹F-NMR measurement was carried out on the obtained compound(12), and the structure was identified from the following results.

Identification Data

¹H-NMR (acetone-D₆): δ [ppm] 0.90 to 1.20 (3H), 1.60 to 2.00 (4H), 3.55to 4.20 (15H)

¹⁹F-NMR (acetone-D₆): δ [ppm] = -55.5 to -51.5 (9F), -78.5 (2F), -80.5(2F), -91.0 to -88.5 (18F)

Example 7

A compound represented by the following formula (13) (4.0 g) wasobtained in the same manner as in Example 1 except that 1,4-butanediolwas used in place of ethylene glycol used in Example 1.

(In the formula (13), p is 4.5 and q is 4.5.)

¹H-NMR and ¹⁹F-NMR measurement was carried out on the obtained compound(13), and the structure was identified from the following results.

Identification Data

¹H-NMR (acetone-D₆): δ [ppm] 0.90 to 1.20 (3H), 1.60 to 2.00 (6H), 3.55to 4.20 (15H)

¹⁹F-NMR (acetone-D₆): δ [ppm] = -55.5 to -51.5 (9F), -78.5 (2F), -80.5(2F), -91.0 to -88.5 (18F)

Comparative Example 1

Fomblin Z-tetraol manufactured by Solvay Solexis that is represented bythe following formula (14) was used.

(In the formula (14), p is 9.0 and q is 9.0.)

Comparative Example 2

A compound represented by the following formula (15) was synthesized bythe method described in Patent Document 1.

(In the formula (15), p is 4.5 and q is 4.5.)

Comparative Example 3

A compound represented by the following formula (16) was synthesized bythe method described in Patent Document 2.

(In the formula (16), p is 4.5 and q is 4.5.)

On the compounds of Comparative Examples 1 to 3 obtained as describedabove, ¹H-NMR and ¹⁹F-NMR measurement was carried out and the structureswere identified.

In addition, the number-average molecular weights of the compounds ofExamples 1 to 7 and Comparative Examples 1 to 3 were obtained by theabove-described ¹H-NMR and ¹⁹F-NMR measurement. The results are shown inTable 1.

TABLE 1 Compound Number-average molecular weight Example 1 (5) 1157Example 2 (8) 1150 Example 3 (9) 1257 Example 4 (10) 1357 Example 5 (11)1213 Example 6 (12) 1171 Example 7 (13) 1185 Comparative Example 1 (14)1964 Comparative Example 2 (15) 1113 Comparative Example 3 (16) 1233

Next, solutions for forming a lubricating layer were prepared using thecompounds obtained in Examples 1 to 7 and Comparative Examples 1 to 3 bya method to be described below. In addition, lubricating layers ofmagnetic recording media were formed using the obtained solutions forforming a lubricating layer by a method to be described below, andmagnetic recording media of Examples 1 to 7 and Comparative Examples 1to 3 were obtained.

Solutions for Forming Lubricating Layer

The compounds obtained in Examples 1 to 7 and Comparative Examples 1 to3 were dissolved in VERTREL (registered trademark) XF (trade name,manufactured by Dupont-Mitsui Fluorochemicals Co., Ltd.), which is afluorine-based solvent, diluted with VERTREL XF, such that the filmthicknesses became 9 Å to 10 Å when applied onto protective layers, andused as solutions for forming a lubricating layer.

Magnetic Recording Media

Magnetic recording media each having an adhesive layer, a soft magneticlayer, a first underlayer, a second underlayer, a magnetic layer and aprotective layer sequentially provided on a substrate having a diameterof 65 mm were prepared. As the protective layer, a carbon layer wasused.

The solutions for forming a lubricating layer of Examples 1 to 7 andComparative Examples 1 to 3 were applied onto the protective layers ofthe magnetic recording media, in which the individual layers up to theprotective layer had been formed, by the dipping method. The dippingmethod was carried out under conditions of an immersion speed of 10mm/sec, an immersion time of 30 seconds and a lifting speed of 1.2mm/sec.

After that, the magnetic recording media to which the solutions forforming a lubricating layer had been applied were put into athermostatic chamber (120° C.) and heated for 10 minutes to remove thesolvent in the solutions for forming a lubricating layer, therebyforming lubricating layers on the protective layers and obtainingmagnetic recording media.

The film thicknesses of the lubricating layers in the magnetic recordingmedia of Examples 1 to 7 and Comparative Examples 1 to 3 obtained asdescribed above were measured using FT-IR (trade name: Nicolet iS50,manufactured by Thermo Fisher Scientific). The results are shown inTable 2.

In addition, a wear resistance test and a chemical substance resistancetest were carried out as described below on the magnetic recording mediaof Examples 1 to 7 and Comparative Examples 1 to 3.

Wear Resistance Test

An alumina sphere having a diameter of 2 mm, which was a contact, wasslid on the lubricating layers of the magnetic recording media using apin-on disc-type friction wear tester at a load of 40 gf and a slidingspeed of 0.25 m/sec., and the friction coefficients of the surfaces ofthe lubricating layers were measured. In addition, the sliding timesuntil the friction coefficients of the surfaces of the lubricatinglayers sharply increased were measured. The sliding time until thefriction coefficient sharply increased was measured four times for thelubricating layer of each magnetic recording medium, and the averagevalue (time) was used as an index of the wear resistance of a lubricantcoating.

The results of the magnetic recording media using the compounds ofExamples 1 to 7 and the compounds of Comparative Examples 1 to 3 areshown in Table 2. Evaluation of the wear resistance by the sliding timeuntil the friction coefficient sharply increased was carried out asdescribed below.

-   AA (Excellent): 650 seconds or longer-   A (Favorable): 550 seconds or longer and shorter than 650 seconds-   B (Permissible): 450 seconds or longer and shorter than 550 seconds-   C (Impermissible): Shorter than 450 seconds

The time until the friction coefficient sharply increased can be used asan index of the wear resistance of the lubricating layers for the reasonto be described below. The lubricating layers of the magnetic recordingmedia are getting worn due to the use of the magnetic recording media.This is because, once the lubricating layer disappears due to friction,the contact and the protective layer come into direct contact with eachother and the friction coefficient sharply increases. The time until thefriction coefficient sharply increased is also considered to correlatewith friction tests.

Chemical Substance Resistance Test

Contamination of the magnetic recording media due to an environmentalsubstance that generated a contamination substance underhigh-temperature environments was inspected by the method to bedescribed below. Si ions were used as the environmental substance, andthe amount of Si adsorbed was measured as the amount of thecontamination substance that was generated by the environmentalsubstance and contaminated the magnetic recording media.

Specifically, the magnetic recording medium, which was an evaluationsubject, was held under a high-temperature environment of a temperatureof 85° C. and a humidity of 0% in the presence of siloxane-based Sirubber for 240 hours. Next, the amount of Si present on and adsorbed tothe surface of the magnetic recording medium was analyzed and measuredusing secondary-ion mass spectrometry (SIMS), and the degree ofcontamination by Si ions was evaluated from the amount of Si adsorbed.The evaluation of the amount of Si adsorbed was evaluated using anumerical value when the result of Comparative Example 1 was regarded as1.00. The results are shown in Table 2.

Comprehensive Evaluation

As comprehensive evaluation, compounds for which the evaluated resultswere comprehensively favorable were indicated by AA (excellent), andcompounds for which the results were poor were indicated by C(impermissible) in Table 2.

TABLE 2 Compound Film thickness (Å) Time until the friction coefficientsharply increased (sec) Wear resistance Amount of Si adsorbedComprehensive evaluation Example 1 (5) 9.5 942 AA 0.52 AA Example 2 (8)9.5 910 AA 0.48 AA Example 3 (9) 9.5 922 AA 0.43 AA Example 4 (10) 9.5899 AA 0.40 AA Example 5 (11) 10.0 927 AA 0.45 AA Example 6 (12) 9.5 912AA 0.44 AA Example 7 (13) 9.5 932 AA 0.50 AA Comparative Example 1 (14)10.0 385 C 1.00 C Comparative Example 2 (15) 9.5 529 B 0.82 CComparative Example 3 (16) 10.0 438 B 0.68 C

As shown in Table 2, in the magnetic recording media of Examples 1 to 7,the sliding times until the friction coefficient sharply increased werelong and the wear resistance was favorable compared with the magneticrecording media of Comparative Examples 1 to 3. In addition, as shown inTable 2, in the magnetic recording media of Examples 1 to 7, the amountsof Si adsorbed were small and the magnetic recording media were lesslikely to be contaminated by the environmental substance under thehigh-temperature environment compared with the magnetic recording mediaof Comparative Examples 1 to 3.

In more detail, in Comparative Example 1 and Comparative Example 3 inwhich no alkoxy group having 1 to 10 carbon atoms was present, terminalgroups each having two hydroxy groups were present at both terminals ofthe perfluoropolyether chain, and the terminal groups bonded to bothterminals were the same as each other, the wear resistance and thechemical substance resistance were not sufficient. Particularly, inComparative Example 1 in which the two hydroxy groups in the terminalgroup bonded to different carbon atoms, and the carbon atoms to whichthe hydroxy groups bonded were bonded to each other, the wear resistancewas poor.

In addition, in Comparative Example 2 in which an alkoxy group having 1to 10 carbon atoms was present at one terminal of the perfluoropolyetherchain, two hydroxy groups were included at the other terminal, and theindividual hydroxy groups bonded to different carbon atoms, but thecarbon atoms to which the hydroxy groups bonded were bonded to eachother, the wear resistance and the chemical substance resistance werenot sufficient.

From these facts, it is assumed that, in the magnetic recording media ofExamples 1 to 7, excellent wear resistance and chemical substanceresistance could be obtained, since the lubricating layers included acompound in which an alkoxy group having 1 to 10 carbon atoms waspresent at one terminal of the perfluoropolyether chain, and the otherterminal had a terminal group in which two hydroxy groups bonded todifferent carbon atoms, and the carbon atoms to which the hydroxy groupsbonded were bonded to each other through a linking group including anether bond.

INDUSTRIAL APPLICABILITY

The present invention provides a fluorine-containing ether compound thatis capable of forming lubricating layers having excellent chemicalsubstance resistance and wear resistance in spite of a thin thicknessand can be preferably used as a material for lubricants for magneticrecording media.

The use of a lubricant for a magnetic recording medium containing thefluorine-containing ether compound of the present invention makes itpossible to form lubricating layers capable of realizing excellentchemical substance resistance and wear resistance in spite of a thinthickness.

Reference Signs List 10 Magnetic recording medium 11 Substrate 12Adhesive layer 13 Soft magnetic layer 14 First underlayer 15 Secondunderlayer 16 Magnetic layer 17 Protective layer 18 Lubricating layer

1. A fluorine-containing ether compound represented by the followingformula (1),

(in the formula (1), R¹ is an alkoxy group having 1 to 10 carbon atoms,R² is a perfluoropolyether chain, R³ is —OCH₂CH(OH)CH₂O(CH₂)_(m)OH (m inthe formula is an integer of 2 to 4)).
 2. The fluorine-containing ethercompound according to claim 1, wherein R² in the formula (1) isrepresented by any one of the following formulae (2) to (4),

(in the formula (2), p represents 1 to 30, and q represents 0 to 30),(in the formula (3), r represents 1 to 30), and (in the formula (4), srepresents 1 to 20).
 3. The fluorine-containing ether compound accordingto claim 1 that is any one of compounds represented by the followingformulae (A) to (F),

(in the formula (A), p represents 1 to 30, and q represents 0 to 30),(in the formula (B), r represents 1 to 30), (in the formula (C), srepresents 1 to 20), (in the formula (D), p represents 1 to 30, and qrepresents 0 to 30), (in the formula (E), p represents 1 to 30, and qrepresents 0 to 30), and (in the formula (F), p represents 1 to 30, andq represents 0 to 30).
 4. The fluorine-containing ether compoundaccording to claim 1, wherein a number-average molecular weight thereofis in a range of 500 to
 10000. 5. A lubricant for a magnetic recordingmedium, comprising: the fluorine-containing ether compound according toclaim
 1. 6. A magnetic recording medium, wherein at least a magneticlayer, a protective layer and a lubricating layer are sequentiallyprovided on a substrate, and the lubricating layer contains thefluorine-containing ether compound according to claim
 1. 7. The magneticrecording medium according to claim 6, wherein the lubricating layer hasan average film thickness of 0.5 nm to 3 nm.